Can I see some ID?

In Illinois, where I now live, all new residents are required to obtain an Illinois driver's license or identification card within 90 days of arrival, surrendering the identification from the state where they lived before. In the Land of Lincoln, identity is clear: either you're an Illinoisan or you're not.

But what about identity in Judaism? Obviously, Jewish identity is a lot more fluid than something like state residency. And the discussion about it touches many fields, one of which is genetics.

In Sam Kean's enlightening book The Violinist's Thumb: And Other Lost Tales of Love, War, and Genius, as Written by Our Genetic Code, the author makes the case that most things in our lives - including our religious identities - are determined by our DNA.

In a fascinating chapter on cultural genetics, Kean reveals how scientists have used DNA (those tiny molecules containing genetic codes for all living organisms) to untangle some of the mysteries of Jewish lineage. He tells of the Biblical division between Jews into the nations of Judah and Israel, which most scholars agree occurred some time between 926 and 922 BCE. He claims that because these two tribes functioned as independent states, each with their own kingdoms, customs, and laws, they probably developed their own distinct genetic markers. This tends to happen when people marry within their own ethnic circles.

Eventually, though, the kingdoms of Judea and Israel dissolved and Jews dispersed throughout the world. Judaism is now practiced by more than 14 million people who live in almost every part of the globe. One would logically assume that the common DNA Jews once shared has mitigated over time. But this hasn't stopped scientists from trying to trace international Jewish groups back to their original kingdoms. And as a matter of fact, it just got a whole lot easier.

In the past few decades, scientists have discovered genetic patterns among Ashkenazi, Sephardi, and Mizrahi Jews that can be traced farther back than ever thought possible. In doing so, they've determined that Jewish tribal associations have largely persisted through time. There is concrete evidence that Jewish tribal groups may be linked through their DNA. This inter-generational genetic bond is especially true for Cohanim, the supposed descendants of Moses' brother Aaron.

According to Jewish tradition, the Cohanim lineage is passed down from father to son. As it happens, there's another gene that does this: the Y-Chromosome. By studying this male-specific chromosome, scientists have found that Cohanim around the world - from Ancient Egypt to Evanston, Medieval Heidelberg to modern Highland Park - all share a similar chromosomal trait, indicating that they do indeed descend from a single patrilineal line. Further study has revealed that the origin of this Y-Chromosome, known as the "Y-Chromosomal Aaron," originated in a human that lived roughly during the time of Moses. It's the perfect example of religious tradition confirmed through science.

The recent discovery of the Y-Chromosomal Aaron has also helped scientists delve deeper into the notion of the Twelve Lost Tribes of Israel. In Africa, the Lemba tribe of Zimbabwe have long made claim to their Jewish roots. As the legend goes, the Lemba are direct descendants of an Israelite named Buba who led his people out of the Middle East and into the Southern tip of Africa.

Initially, anthropologists wrote off Jewish claims of the Lemba as evidence of "cultural transmission" - the result of Jews and proselytizing Muslims arriving in Africa circa 600 BCE. But the Lemba were adamant, holding firm to their Jewish ancestry. They did not eat pork, they observed a Sabbath similar to that of the Jews, and they even circumcised their male children.

To get to the bottom of this issue, scientists turned to DNA. They drew blood samples from Lemba men, and what they discovered surprised them. Over 10 percent of all Lemba men had the Y-Chromosomal Aaron in their bloodstreams. For members of the tribe's oldest families - those with priestly rites - that number was 50 percent. The Lemba could indeed claim descendance from Moses' brother Aaron. Science was on their side.

So is Jewish identity simply a matter of genes? Of course not. Identity is much more than physical and genetic make up. About.com defines identity as "the stable understanding of oneself, including one's own traits, preferences, thought patterns, strengths, and weaknesses." I think you can say the same about Jewish identity. It too is a combination of characteristics and traits that, when combined, define a person as a Jew.

Few of these traits are genetic. Many are spiritual, like the traditions we hold and the beliefs we choose to follow. A few are historical, like the past we consider ourselves a part of and the events we choose to honor. Still others are cultural, like the music we listen to, and even the foods we like. Some of these things are passed down from our fathers and mothers. Many we develop on our own.

The biggest thing to take away from all this is that it doesn't matter how one's Jewish identity comes to be, but why. Judaism requires a great deal from its practitioners: an adherence to certain laws, the pursuit of earthly justice, a commitment to repair the world. And those who choose to identify as Jewish do so because they care deeply about these values. Even more, they want future generations to care about them too. After all is said and done, the most important tradition is that we continue to pass these values down from generation to generation. We don't need science to tell us that.

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